There was a need to help controllers make a transition from “miles in trail” metering to “time based” metering during heavy traffic conditions. Time based metering has been shown to be more efficient, but difficult for controllers to visualize. This tool provided the necessary information for en route controllers in arrival sectors to more efficiently sequence aircraft in the arrival stream and have them arrive at a fix at a specific time of arrival to the Terminal airspace boundary. By providing a list of incoming aircraft in the proper sequence it relieved the controller of the burden associated with developing the final sequence. Once in the arrival stream the controller was provided with not only the scheduled time of arrival at the fix, but also the amount of time that each aircraft must be delayed so that the temporal spacing between aircraft provides the optimum flow through the fix into Terminal airspace. Much of the support for the tool came from the traffic management unit that sets parameters in the tool as well as determines where and when the tool will be used depending on attributes of traffic. The tool acts as an intermediary between the controller and traffic manager and provides a transition between the strategic plan for traffic flow to the tactical domain of the sector controller that executes the plan.
The TMA tool was part of the NASA Center TRACON Automation System program and was developed during the 1990s. TMA was operationally introduced to the field as part of the Free Flight Phase I program circa 2001.
This application of automation made a positive contribution to field operations and was accepted fairly quickly by the various facilities and individuals. There was some initial resistance to use of a paradigm other than miles-in-trail since that mode of operation is easy to visualize on a spatial display such as a radar scope. Once facilities adopted use of the tool it became apparent that sector throughput was increased without undue hardship on the controller. With a little practice the controllers found ways to absorb the specified delays to meet the scheduled time of arrival. The sequence provided by TMA was generally a stable listing and provided an answer for the controller’s dilemma regarding how to arrange aircraft efficiently in the arrival stream.
Users were convinced quickly after TMA was fielded that it made a positive contribution to capacity of the airspace, improved the metering process for the downstream terminal facility, and relieved workload for the controller, with a few trade-offs. The information was easy to understand, was stable, and provided a workable and valuable solution to the metering problem. The tool provided the controllers with a small challenge to translate delay times into aircraft vectors or speed changes, but this was quickly overcome with practice and sharing solutions among peers.
This is a success story. The tool provided a solution for the metering problem in the arrival stream and was used in the intended manner for the intended purpose. The outcome in terms of efficiency metrics met the expectations of the tool.
During the final stages of tool development there was considerable input from expert controllers that specialized in the metering problem. They spent considerable time working with software developers to assure that the dynamic characteristics of the tool met the needs of the controller while improving the flow of arrival traffic. The tool was simplified to minimize the parameters that were manipulated by the controller to reduce the complexity of the solution. Significant input was also received from the traffic flow domain so that the tool helped both domains increase productivity and collaboration.
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